Cerebral Cortex Advance Access originally published online on November 24, 2004
Cerebral Cortex 2005 15(8):1123-1133; doi:10.1093/cercor/bhh211
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© Oxford University Press 2004; all rights reserved
Prefrontal-hippocampal dynamics involved in learning regularities across episodes
1 Experimental Neuropsychology Unit, Department of Psychology, Saarland University, Saarbrücken, Germany and 2 Department of Neuroradiology, Saarland University Hospital, Homburg, Germany
Address correspondence to Christian F. Doeller, Saarland University, Department of Psychology, Experimental Neuropsychology Unit, PO Box 15 11 50, Saarbrücken D-66041, Germany. Email: c.doeller{at}mx.uni-saarland.de.
Using functional magnetic resonance imaging, the neural correlates of context-specific memories and invariant memories about regularities across episodes were investigated. Volunteers had to learn conjunctions between objects and positions. In an invariant learning condition, positions were held constant, enabling subjects to learn regularities across trials. By contrast, in a context-specific condition object–position conjunctions were trial unique. Performance increase in the invariant learning condition was paralleled by a learning-related increase of inferior frontal gyrus activation and ventral striatal activation and a decrease of hippocampus activation. Conversely, in the context-specific condition hippocampal activation was constant across trials. We argue that the learning-related hippocampal activation pattern might be due to reduced relational binding requirements once regularities are extracted. Furthermore, we propose that the learning-related prefrontal modulation reflects the requirement to extract and maintain regularities across trials and the adjustment of object–position conjunctions on the basis of the extracted knowledge. Finally, our data suggest that the ventral striatum encodes the increased predictability of spatial features as a function of learning. Taken together, these results indicate a transition of the relative roles of distinct brain regions during learning regularities across multiple episodes: regularity learning is characterized by a shift from a hippocampal to a prefrontal–striatal brain system.
Key Words: fMRI • hippocampus • learning • prefrontal cortex • ventral striatum
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